The present invention relates to a work pallet positioning and fixing device that positions and fixes a work pallet above a base member in the horizontal direction and in the vertical direction, and in particular relates to such a device that fixes the work pallet by manually driving a plurality of clamp bolts.
Conventionally, in the technical field of peripheral devices for machine tools, various types of work pallets for fixing workpieces to be supplied to machining, and work pallet positioning and fixing devices that position and fix such work pallets to base members, have been widely put into practical use.
For example, with the work pallet positioning and fixing device described in Patent Document #1, four set of ball lock type clamp mechanisms are provided on the base member side, while four ring members corresponding to the four clamp mechanisms are provided to the work pallet, so that the work pallet is positioned in the horizontal direction and in the vertical direction, and is clamped.
The clamp mechanism is constituted so as to be driven to clamp condition by laminated plate springs, and to be driven to clamp release condition by the hydraulic force of a hydraulic cylinder. With this positioning and fixing device, the work pallet is positioned in the horizontal direction and in the vertical direction by one set of a clamp mechanism and a positioning mechanism on a reference side, and is restricted so as not to rotate around the axis of the reference side clamp mechanism by another set of a clamp mechanism that is located in a diagonal relationship with the clamp mechanism and positioning mechanism on the reference side.
On the other hand, with the work pallet positioning and fixing device described in Patent Document #2, four set of ball lock type clamp mechanisms are provided on the base member side, while four ring members corresponding to the four clamp mechanisms are provided to the work pallet, so that the work pallet is positioned in the horizontal direction and in the vertical direction, and is clamped. The clamp mechanism is constituted so as to be driven to clamp condition by laminated plate springs, and to be driven to clamp release condition by the hydraulic force of a hydraulic cylinder.
In each of the clamp mechanisms, tubular axis portion having annular tapered surface on the outer circumferential surface is provided to the base member. An annular engagement portions that can be elastically deformed in the direction to increase its external diameter is formed on a ring member fixed to work pallet, and it is arranged to position the work pallet in the horizontal direction by mounting the work pallet onto the base member from above, fitting the annular engagement portions of the ring members over the tubular axis portions respectively, and engaging the annular engagement portions by the clamping force generated by the clamp mechanisms to the annular tapered surfaces of the tubular axis portions in the closely engaged state by means of elastically deforming the annular engagement portions in the direction to increase their external diameters.    Patent Document #1: Japanese Laid Open Patent Publication 2001-38564    Patent Document #2: Japanese Laid Open Patent Publication 2003-39264
With the devices of Patent Documents #1 and #2, hydraulic cylinders that are equipped with laminated plate springs are applied as the actuators for the clamp mechanisms. However the manufacturing cost becomes extremely high, since the hydraulic cylinders are large in size and also their structure is complicated. On the other hand, if a construction is adopted in which the work pallet is fixed to the base member by the clamping force of clamp bolts that are screwed by manual operation, then it becomes possible to make the clamp mechanism more compact, and to reduce the manufacturing cost.
Now, if a positioning mechanism is employed, as with the work pallet positioning and fixing device of Patent Document #2, in which annular engagement portions are deformed by the clamping force in the direction to increase their external diameters, and are thereby engaged to tapered engagement surfaces, then, since the clamping force of clamp bolts is comparatively weak as compared to the clamping force of hydraulic cylinders that are internally equipped with laminated plate springs or of hydraulic cylinders of a normal type, accordingly the function of elastically deforming the annular engagement portions will be reduced, and there is a possibility that the accuracy of positioning in the horizontal direction will be reduced.
Thus, while it may be considered to set the rigidity of the annular engagement portions in the horizontal direction lower, if this is done, it becomes difficult to ensure the positioning accuracy in the horizontal direction. For this reason, it is a technically difficult problem to provide a structure in which it is possible to deform the annular engagement portions elastically by the clamping force of clamp bolts that are driven manually to be tightened up, while still ensuring their rigidity.
If a construction is employed for the clamping and positioning mechanism in which a reference member is provided to the base member, and a flange portion formed on this reference member is fixed to the base member by a plurality of clamp bolts, then, if the diameter of the flange portion is increased, the reference member is increased in size, and its manufacturing cost becomes high.